The present invention relates, in general to alarms and, more particularly, to circuits for controlling alarms.
Conventional smoke detectors provide an audible alarm after the smoke density in an area increases above a predetermined minimum threshold level. Smoke from cooking or persons smoking can cause nuisance or false alarms to occur. Accordingly, many smoke detectors include a silencing feature for temporarily silencing the smoke detector.
Such silencing features can be activated by a push button, thereby disabling the smoke detector for a predetermined time period of, for example, fifteen minutes. During this time period, the smoke condition will usually dissipate, and at the end of the silencing period the detector will return to a normal mode of operation.
Some prior art smoke detectors implement the silencing feature by rendering the smoke detector inoperative. This can be dangerous in the event that a hazardous fire develops after activating the silence feature. Other prior art smoke detectors increase the smoke threshold level necessary for generating an alarm. This is undesirable since it diminishes the smoke sensitivity of the detector during the silence mode of operation. Further, these prior art smoke detectors do not provide a means for canceling the silence mode and remain in the silence mode for a fixed predetermined period.
Accordingly, it would be advantageous to have an alarm circuit that includes a silencing feature for temporarily silencing the alarm circuit. It would be of further advantage for the alarm circuit to remain operative during the silencing period. In addition, it would be advantageous for the alarm circuit to have a feature for canceling the silencing feature before the expiration of the silencing period.